This invention relates to isolation mounts. More particularly, this invention relates to an isolation mount such as an engine mount providing a plurality of spring rates under various loading conditions imparted by an engine that is supported by the mount.
While the following discussion talks in terms of an engine mount such is by way of example only. It is to be understood that other applications for the described engine mount are also contemplated such as in rock drills, compressors, etc.
Currently, engines in various applications are mounted by means of relatively resilient shock mounts. These mounts are designed to have good isolation properties to minimize the transmission of vibration, etc., from the engine to a supporting structure, such as the vehicle frame. Currently, the mounts typically utilize a pair of outer and inner annular metal bushings having an annular resilient bushing of rubber material compressed therebetween. The inner bushing is fitted over a stub shaft which projects from the engine that is being supported. The outer bushing, in turn, is supported by a mount housing which may be typically fixed to a frame, such as a vehicle frame. A plurality of such mounts are used to support an engine.
An example of a prior art mount is shown in U.S. Pat. No. 3,770,231, assigned to the same Assignee hereof.
Current rubber shock mounts provide a single linear spring rate for deflections imposed thereon by engine operation. This is undesirable, in that while a relatively soft and linear spring rate is required for normal load conditions on the shock mount, shock loading can detrimentally affect the rubber mount material, causing fatigue failure. Thus, it is very desirable to have a double or even triple rate mount that would effectively: give a relatively soft linear spring rate for normal loads; and then respond with a higher or stiffer spring rate or rates when subjected to shock loads. In essence, what is desired is to have a double or even triple rate mount.